Thermostatic valve arrangements are well known in the art, and a conventional thermostatic valve arrangement is used to adjust the temperature of a fluid coolant provided to an internal combustion engine in order to maintain a desired operating temperature of the engine. In general, each thermostatic valve arrangement includes a main valve assembly for controlling coolant flow from a coolant radiator into a mixing chamber, a bypass valve assembly for controlling coolant flow directly from the engine into the mixing chamber, and a thermostatic assembly for inversely adjusting the main valve assembly and the bypass valve assembly for adjusting the two coolant flows into the mixing chamber.
Conventional operation of such conventional thermostatic valve arrangements is as follows. During initial operation of the engine when the engine is in a cold state, flow through the main valve assembly of the thermostatic valve arrangement is closed and flow through the bypass valve assembly is open whereby coolant flows from the fluid passage for the engine outlet directly to the fluid passage for the engine intake without passing through the coolant radiator. When the temperature of the coolant reaches the "opening" temperature--or "reaction" temperature--of the thermostatic element of the thermostatic assembly, flow from the radiator through the main valve assembly is opened and flow through the bypass valve assembly is reduced. Thus, the thermostatic valve assembly regulates the temperature of the coolant flowing into the engine intake by changing as a function of its position the cross-sectional flow through the main valve assembly and the cross-sectional flow through the bypass valve assembly, whereby relatively cool coolant from the coolant radiator and relatively warm coolant coming from the engine outlet are mixed in the mixing chamber to obtain a desired temperature. Thereafter the mixture having the desired temperature flows to the engine intake. During a maximum cooling operation, flow through the bypass valve assembly is closed and flow through the main valve assembly is completely opened.
Based on the foregoing, it can be seen that such conventional thermostatic valve arrangements have three operating states, i.e., an initial state wherein the bypass valve assembly is open and the main valve assembly is closed, an operating state wherein both valve assemblies are open to varied extents, and a cooling state wherein the bypass valve assembly is closed and the main valve assembly is fully open.
An improvement in such thermostatic valve arrangements is disclosed by DE 195 45 081 A1 wherein the thermostatic valve arrangement therein further blocks fluid flow through the bypass valve assembly during engine warm up when the engine is in a cold state and running at idle. With particular reference to the Figure of this reference, this improvement is accomplished in the bypass valve assembly by use of a bypass spring (31) that urges a bypass valve disc (30) slidably disposed about a shaft (25) toward a retaining ring (28) secured on the end of the shaft and into covering relation with the fluid passage (14) for the engine outlet, which consequently permits the engine to reach a desired operating temperature more quickly than possible with the aforementioned thermostatic valve arrangements. Furthermore, in order to prevent local overheating of the engine when operated above idle rpm in the cold state, the bypass valve assembly functions as an overpressure valve whereby the bypass valve disc and the bypass spring initially yield to a predetermined differential pressure between the fluid passage for the engine outlet and the fluid passage for the engine intake. A cross-sectional flow through the bypass is thus created when the predetermined differential pressure is exceeded due to the higher rpm of the engine when operated above idle rpm in the cold state. When the differential pressure reaches a second, higher predetermined differential pressure, the bypass valve disc engages an abutment member (26). The abutment member includes a sleeve (29) that is slidably disposed about the shaft and extends towards the retaining ring and on which the bypass valve disc actually slides. A spring (27) urges the abutment member into engagement with the retaining ring and, when the bypass valve disc engages the abutment member, the spring assists the bypass spring in resisting further displacement of the bypass valve disc from the retaining member.
The thermostatic valve arrangement of DE 195 45 081 A1 furthermore provides a minimal coolant bypass flow even when the bypass valve assembly is closed by the provision of openings (34) in the bypass valve disc, the total cross-sectional flow through which is less than the maximum cross-sectional flow through the fluid passage for the engine outlet. These openings thereby provide a minimum coolant bypass flow when the bypass valve assembly is closed. Furthermore, the abutment member extends radially outwardly sufficient to sealingly cover the openings when the bypass valve disc is fully open and in engagement with the abutment member. The bypass valve disc also includes a collar (32) which assures that the bypass flow, including the bypass flow through the openings, does not flow directly to the engine intake but, instead, is directed towards the thermostatic element for proper functioning of the thermostatic element.
In comparison with the thermostatic valve arrangement of the present invention, the thermostatic valve arrangement disclosed in DE 195 45 081 A1 includes a thermostatic assembly, a spring support member, a main valve assembly, a bypass valve assembly, and a valve support assembly. Furthermore, the thermostatic valve of DE 195 45 081 A1 has similar operating characteristics to those of the thermostatic valve arrangement of the present invention. However, the thermostatic valve arrangement of the present invention achieves these similar results in an alternative, simplified, and cost effective manner with modifications to the bypass valve assembly and valve support assembly as discussed in detail below.